nanog mailing list archives
Re: Broken PMTU (was: Who does source address validation? (was Re:what's that smell?))
From: Valdis.Kletnieks () vt edu
Date: Thu, 10 Oct 2002 01:11:05 -0400
On Thu, 10 Oct 2002 00:55:24 +0200, Iljitsch van Beijnum said:
You can also get around this by making the first hop the one with the lowest MTU. This is no fun for ethernet-connected stuff, but for dial-up this is easy. Then this box will announce a smaller TCP MSS when the connection is established and there aren't any problems.
Or equivalently, just nail the MSS size for off-site connections down to 512, and accept that you have to send 3 times as many packets as you probably should. As far as I can tell from when pMTU *does* work because all parties concerned actually use reasonable addresses and don't filter 'icmp frag needed', you end up with one of 3 results most of the time: 1) You get a clear 1500 end-to-end. 2) You get an MTU of 1460 because of tunneling. 3) You end up racheted down to 576 because of some ancient IP stack someplace (older versions of end-user SLIP/PPP are famous for this) -- Valdis Kletnieks Computer Systems Senior Engineer Virginia Tech
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Current thread:
- Re: Who does source address validation? (was Re: what's that smell?), (continued)
- Re: Who does source address validation? (was Re: what's that smell?) Stephen J. Wilcox (Oct 09)
- Re: Who does source address validation? (was Re: what's that smell?) Joe Abley (Oct 09)
- Re: Who does source address validation? (was Re: what's that smell?) David Schwartz (Oct 09)
- Re: Who does source address validation? (was Re: what's that smell?) Stephen Stuart (Oct 09)
- Re: Who does source address validation? (was Re: what's that smell?) alex (Oct 09)
- Re: Who does source address validation? (was Re: what's that smell?) David Schwartz (Oct 09)
- Re: Who does source address validation? (was Re: what's that smell?) alex (Oct 09)
- Re: Who does source address validation? (was Re: what's that smell?) Joe Abley (Oct 09)
- Re: Who does source address validation? (was Re: what's that smell?) Stephen J. Wilcox (Oct 09)
- Re: Who does source address validation? (was Re: what's that smell?) Sean Donelan (Oct 09)
- Re: Who does source address validation? (was Re: what's that smell?) Stephen J. Wilcox (Oct 09)
- Re: Broken PMTU (was: Who does source address validation? (was Re:what's that smell?)) Iljitsch van Beijnum (Oct 09)
- Re: Broken PMTU (was: Who does source address validation? (was Re:what's that smell?)) Valdis . Kletnieks (Oct 09)
- Re: Broken PMTU (was: Who does source address validation? (was Re:what's that smell?)) Stephen J. Wilcox (Oct 10)
- Re: Broken PMTU (was: Who does source address validation? (was Re:what's that smell?)) Tony Rall (Oct 10)
- Re: Who does source address validation? (was Re: what's that smell?) Valdis . Kletnieks (Oct 09)
- Re: Who does source address validation? (was Re: what's that smel l?) Steve Francis (Oct 09)
- Re: Who does source address validation? (was Re: what's that smel l?) Valdis . Kletnieks (Oct 09)
- Re: Who does source address validation? (was Re: what's that smel l?) Hank Nussbacher (Oct 10)
- Re: Who does source address validation? (was Re: what's that smell?) Richard A Steenbergen (Oct 10)
- Re: Who does source address validation? (was Re: what's that smell?) Iljitsch van Beijnum (Oct 10)
- Re: Who does source address validation? (was Re: what's that smell?) Jared Mauch (Oct 10)
- Re: Who does source address validation? (was Re: what's that smell?) Iljitsch van Beijnum (Oct 12)